In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, one parameter in providing good performance and capacity for a given communications protocol in a communications network is the coverage of the communications network.
In a first stage of the deployment of a communications network providing ubiquitous coverage, the operator may target to establish as large population coverage as possible so as to service as many wireless devices as possible. At a later stage, the operator may typically need to upgrade the communications network to meet an increasing traffic capacity demand. Such an upgrade procedure may commonly include providing existing radio access network nodes with new hardware, such as advanced antenna systems, adding mechanism for interference coordination, adding more frequency spectrum (e.g., by providing existing radio access network nodes with an increasing number of antennas as well as an increasing number of radio chains to handle the new spectrum, and adding more radio access network nodes.
Typically, the traffic capacity need in a communications network varies with time, and the operator may need to dimension the communications network to handle so-called busy hours when the traffic demand is the highest. Consider, as an illustrative non-limiting example, an office environment where there may be a need for high capacity during office hours, whereas the need may be much lower during night when only a fraction of the employees, if any, are present in the buildings. Similarly, during commute hours the capacity need may be high at a subway station; just as it may be high in a residential area in the evening, for example due to subscribers consuming streaming services in their homes.
Services may not be provided only by a single radio access technology (RAT). In fact, an operator may be expected to provide network coverage for multiple RATs, such as example Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA), and Long Term Evolution (LTE). In some communications networks, for each RAT, cells on multiple frequencies can be provided. This is illustrated in FIG. 1c. In FIG. 1c radio access network node, or site, 110a is configured to provide network coverage in a first cell 140a on a first carrier frequency f1 and in a second cell 140b on a second carrier frequency f2; radio access network nodes 110b and 110c are configured to provide network coverage in a respective further second cells 140b on the second carrier frequency f2; and radio access network nodes 110d and 110e are configured to provide network coverage in a respective third cell 140c on a third carrier frequency f3.
Radio access network nodes consume energy not only in active mode when serving wireless devices, but also in idle mode when no wireless devices are served. Technology development is expected to reduce power consumption and make the power consumption more directly proportional to the amount of traffic served. Further, the power consumption can be reduced by reducing the transmit power and even switching off a cell (as provided by one or more radio access network nodes) when there is no need for network coverage; when the capacity of a cell is not needed it can thus be switched off. At the same time, it is desirable to provide network coverage so that access to the communications network is available when needed. For example, with reference to the above illustrative non-limiting example, during night-time the need for network capacity for providing streaming services can be low, but the need for network coverage to provide voice services may still be high.
In U.S. Pat. Nos. 9,030,983B2 and 8,996,020B2 methods are presented wherein one or more sites is allowed to be put into sleep mode if this results in an energy saving. Both methods rely on a database that guarantees that there is no loss in coverage loss. The coverage requirement can be supplied through cell planning or through reports from wireless devices. Moreover, although U.S. Pat. Nos. 9,030,983B2 and 8,996,020B2 provide information on what sites to shut down to save energy, these documents fail to disclose when to turn the sites on again. As a result thereof, radio access network nodes are switched on again at random. Alternatively, all radio access network nodes are switched on again, and later, radio access network nodes that are not needed are switched off again.
Hence, there is still a need for an improved cell operation in a wireless communications network.